This invention relates to a multi-capstan haulage winches in general, and more specifically to twin-capstan arrangements having a third capstan associated therewith for delivering line to the twin capstans.
U.S. Pat. No. 3,834,673, entitled Twin Capstan Winches, to Alexander describes a haulage winch comprising twin haulage drum, i.e. twin, multi-groove capstans, and a chain of gears for driving the haulage capstans. The majority of the gears are mounted on shafts which lie in or are adjacent to a substantially horizontal plane in which the axes of the haulage capstans lie.
Although the described winch is an advance over previous winch designs, high bending and compression stresses can occur in the bearings and mounting of the haulage capstans. As the diameter of the capstan increases for accommodating various cable or line diameters and loading requirements, such stresses increase, along with the power supply requirements for driving the twin capstans. This not only necessitates a more expensive system, but also a more massive system of increased dimensions which could pose problems for many applications.
Because of known advantages over conventional reel-tupe drum winches, the twin capstan winches, such as above referenced, have achieved widespread usage. For example, in capstan winches, the line progresses smoothly over the capstans at a speed determined by the driving motor, as only a single layer of line builds on the capstans. The spooling of the line for storage is at relatively low tensions, preventing damage to the line even if the load varies. Still further, the reeling or storage drum can be constructed (or changed) according to the length of the line to be hauled in and may also be situated in a convenient place distant from the capstan unit.
On the other hand, even though a reel-type drum winch may have a tendency to crush the line and must be geared to accommodate the maximum torque on the outer wrap of the line around its drum, a reel-type winch does not require the added expense of a plurality of drum units for implementing an effective system. This is a feature which, absent other considerations, is believed to heretofore have eliminated any advantages obtained by associating a capstan unit with a reel-type drum winch.
Of course, for certain applications wherein circumstances call for independent operation of two separate winding units, a capstan unit may be used in association with a reel-type drum winch for achieving the overall objective. Such a case is an integrated chain-wire rope mooring system wherein a reel-type winch is provided for hauling in and storing the line, and a windlass wildcat is provided for hauling in the chain. By operating the wildcat when the winch is not hauling in, the chain may be deposited in a storage compartment. In such an application, there may be a brief period when both the windlass and the winch are hauling in under power; since both winch and windlass are already available, the operation of the windlass to assist the winch is at no extra system cost. However, it is not believed that capstan units have been associated with reel-type drum winches primarily for reducing the loading on the reel-type drum winch during haul in. The slippage inherent on a capstan type unit, especially on a less than full wrap capstan unit, is believed not to have justified its use for reducing the loading on a reel-type winch.